Use the new predicate support that Evan Cheng added to remove some code

from the DAGToDAG cpp file.  This adds pattern support for vector and
scalar fma, which passes test/Regression/CodeGen/PowerPC/fma.ll, and
does the right thing in the presence of -disable-excess-fp-precision.

Allows us to match:
void %foo(<4 x float> * %a) {
entry:
  %tmp1 = load <4 x float> * %a;
  %tmp2 = mul <4 x float> %tmp1, %tmp1
  %tmp3 = add <4 x float> %tmp2, %tmp1
  store <4 x float> %tmp3, <4 x float> *%a
  ret void
}

As:

_foo:
        li r2, 0
        lvx v0, r2, r3
        vmaddfp v0, v0, v0, v0
        stvx v0, r2, r3
        blr

Or, with llc -disable-excess-fp-precision,

_foo:
        li r2, 0
        lvx v0, r2, r3
        vxor v1, v1, v1
        vmaddfp v1, v0, v0, v1
        vaddfp v0, v1, v0
        stvx v0, r2, r3
        blr

llvm-svn: 24719